stories and people

Core sampling, a truly fascinating world

Rock samples tell the stories of the Earth.

Core sampling, a truly fascinating world

Rock samples tell the stories of the Earth.

Journey to the centre of the Earth

Andrea Ortenzi, Technical Manager of geology laboratories in Bolgiano, is with us
at the Eni research centre in San Donato Milanese, entry point for all samples of
fluids and rock that are picked up by our wells around the world. "To get to know
the history of a reservoir through samples, we must find discover it". What is behind
the discovery of a deposit? Skills, innovation and the spirit of collaboration are
the basis of our success, starting from the technologies for the study of the subsoil.

Exploring the subsoil is an activity that takes advantage of advanced technologies and that often also requires the reproduction of complex geological events in the laboratory.

ANDREA ORTENZI

World samples

The first samples arrived in the Thirties and today constitute a great wealth. Core samples represent a vertical section of our reservoir of hydrocarbons. They tell us about the age of the rock, they measure porosity and permeability and allow the provision of the production of hydrocarbons in time.

Exploration with low environmental impact

Core samples also allow us to understand the environment in which they are deposited. Eni is strongly committed to reducing the environmental impact of its activities and to guarantee the safety of the plant.

From the earth to the laboratory

When core samples arrive in the laboratory they are studied by our technicians. The analysis allows us to reconstruct what happened inside our field over millions of years of its history. Here is how:

Resting samples: first of all, the core samples are photographed, both in normal and ultraviolet light, to see how hydrocarbons are distributed within the rock.

One great little world: the subsequent electron microscope observation makes us see at very high magnification what happened inside the pores of our rock.

Reservoir efficiency index in terrigenous rocks

At least half of all hydrocarbons are contained within the pores of sedimentary rocks made up of fragments of other rocks. Reservoir quality is determined by its original characteristics and the way in which its internal structure has evolved, the study of which belongs to a discipline of geological science known as petrography. Study is on a microscopic scale and samples comprise thin sections of rock examined under both optical and electron microscopes.With patience and passion, the petrographer quantitatively measures critical variables such as grain size within the bedrock, components present at the time of deposition and those which have been generated over history. Furthermore, the size and spatial arrangement of the solid rock are measured "negative" to show the pores that contain the hydrocarbons. Diagenesis, linked to the thermal history of the rock, determines the quality of the reservoir and groups together all the dissolution phenomena of the grains and the precipitation of new minerals inside the pores after the deposition of the original sand. By observing the geometric relationships between the various minerals formed in the pores, aided by specific analyses aimed at determining their formation temperature, it is possible to reconstruct the sequence of such phenomena – the so-called diagenetic history. Once all the ingredients of the “recipe” are available, it allows a prediction to be made concerning the quality of the subject reservoir without a well having to be drilled. The collected quantitative and qualitative information is amalgamated to give a single item of information expressed as an index that indicates the quality of the rock in situ. This is known as the reservoir efficiency index (e-rei) and correlates to the permeability and porosity of the reservoir. The e-rei is sensitive to any changes in diagenesis related to variations in burial and thermal history. It is calculated on a core sample for each sedimentological facies identified in the reservoir and plotted as a trend map (depth and/or temperature). As mentioned previously, the e-rei value can be translated into porosity and permeability values ​​that can be used both by explorers and those responsible for constructing models of deposits to optimise development and production. The importance of this integrated, common effort continues to be recognised even if the distance between a bit of rock and a corporate financial statement sometimes appears immense.

Explore the underground with Gravity Gradiometry

Each type of rock is characterised by certain values of density, which can be reconstructed. Thanks to Gravity Gradiometry (GG) technology, we can obtain valuable information on the type of rocks in the area and on their geometries in the subsoil. Eni has been a pioneer in the use of this type of data since the turn of the millenium.

5,000metres

depth of core sampling

5,000 metres

depth of core sampling

4,000oils

core samples preserved in the Eni research centre in San Donato

4,000 oils

core samples preserved in the Eni research centre in San Donato

200k

containers rock samples stored in the Oil & Gas laboratory

200 k

containers rock samples stored in the Oil & Gas laboratory

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